The present invention relates to a method for the operation of a transverse guiding driver assist system of a motor vehicle.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Tracking systems are known as driver assist systems for the transverse guidance of a motor vehicle to automatically carry out steering interventions. The tracking systems are constructed to enable a motor vehicle, for example on a highway, to automatically track the road course so long as no excessive steering interventions are required. Generally, these types of transverse guiding driver assist systems analyze a future road course, which is determined from environmental or operating data of the motor vehicle. Additional information, for example a street category or the like, can be assigned to this road course.
Constructions are known in which the future road course is determined by a navigation system of the motor vehicle and provided to a control device of the driver assist system, which then deduces the transverse guiding parameters, in particular a steering angle, therefrom. Such a future road course, which is provided by a navigation system, can for example be provided as form elements, which often are referred to as clothoids. These have attributes assigned to them which provide the future road course, concretely the course of the road which is being driven on. The attributes include for example the horizontal curvature in driving direction, the street category, the road surface and the like. Beside the transverse guiding driver assist systems, these data can also be used as environmental data in other vehicle systems.
It is customary to build roads such that they are not perpendicular to the gravity vector transverse to the driving direction, i.e. not absolutely horizontal, for example to allow drainage of rain water. The deviation of the transverse course of the road surface from the horizontal is usually referred to as “road banking”. Roads are often configured such that in curves the incline is directed towards the inside of the curve, whereas in a straight course of the road, the roads or lanes slant towards the right to allow liquid to run off. Accordingly, a change in road banking can occur before a turn, when for example in the case of a road surface which slants towards the right, a left turn soon follows which is inclined towards the inside of the curve.
These changes in road banking mostly occur along relatively short regions of change, for example within a distance of 50 m, to keep the region in which the road is completely or approximately horizontal, as small as possible. Because this change in road banking is not known to a transverse guiding driver assist system, a substantial lateral path deviation sometimes occurs in the case of a change in road banking, for example before a turn. This course deviation is reflected in the environmental and/or operating data of the motor vehicle, which are also used for determining the steering intervention. However, because of the inertia of the control, which is mainly necessary because of comfort criteria, strong deviations accumulate, which can no longer be compensated with the maximal steering torques described by the system boundaries. As a result, the driver assist system is deactivated (termination of the operation) and a manual intervention becomes necessary. The limits of the permissible steering torques are governed for example by legal regulations, providing for a steering torque limit of for example 3 Nm, which are usually not sufficient when a change in road banking is involved.
It would therefore be desirable and advantageous to provide an improved transverse guiding driver assist system to obviate prior art shortcomings and realize a reliable functioning of the assist function even when the road banking changes.